A wide variety of keyboards are known for use in typewriters, calculators, data entry terminals, remote control terminals and the like. Many of such keyboards employ relatively large keys with relatively large on-center spaces. Often these keys are complex in construction and operate not only to make switch contact, but to provide an operator with a tactile sensation or feedback, whereby the operator is assured of having made switch contact. Such switches employ a wide variety of structures ranging from spring loaded assemblies to dome-type switch elements to provide this tactile feedback signal. Many of such keyboards provide backlighting of the individual keys, so that the keyboard may be used in a darkened environment. Commonly, backlighting is provided by individual light emitting diodes (LEDs) associated with each of the keys. Moreover, it is desirable to provide status indicator lights for some of the keys. Such status indicator lights frequently are not mounted on moveable keys but are positioned adjacent to their associated keys.
For many keyboards, liquid spillage and debris falling into the keyboard are serious problems. Liquids will normally drain down around the key systems and into the keyboard structure itself. Such liquids may be damaging as the liquid may interfere with the optical channels and, in a backlighted keyboard, block passage of the light. Moreover, there is always the problem of liquids shorting out the circuits in the keyboard. These problems are particularly acute for keyboards utilized with medical equipment, such as medical ultrasound.
A problem that frequently arises in medical ultrasound applications is that the operator is required to operate the keyboard immediately after applying an electrically conductive gel to the patient. Occasionally, the gel is not completely removed from the operator's hands and a residue is left on the individual keys of the keyboard. Also, there is a possibility that other undesirable contaminants may be transferred to the keys of the keyboard by the operator's hands and fingers. For these reasons, it is desirable to be able to wash the keyboard easily and completely without damaging the underlying circuitry.
A tactile feedback through "over-travel" of the keys has been determined to be desirable in a keyboard. This "over-travel" effect renders the keyboard ergonomically more desirable by being less tiring to use. Also, the user is reassured that the key stroke has produced the desired effect.
Difficulties have been encountered in the past in developing a keyboard which provides the desired tactile feedback through a full travel key, is completely sealed against liquid penetration, and also provides the desired backlighting and status indicator lights. Often, the provision of a light pipe for a status indicator or lights for backlighting requires penetration of a membrane which otherwise would seal the keys from the underlying printed circuit board or other electrical connections. These areas of penetration provide opportunities for liquids to seep into the electrical connections. Also, in the past, some difficulty has been encountered in providing backlighting in conjunction with full travel keys. Finally, most existing backlighted keyboards cannot be easily cleaned without risking damage to the electrical circuitry.